Wide-band loudspeaker



p 1955 e. BUCHMANN 2,717,047

WIDE-BAND LOUDSPEAKER Filed Dec. 3, 1952 Rig. 1 F y, 2

INVENTOR GERHARD BUCHMA ATTORNEY United States Patent 6 1 2,717,047 WIDE-BAND LOUDSPEAIER Gerhard Buchmann, Eutingen, Baden, Germany, assignor to International Standard Electric Corporation, New

York, N. Y., a corporation of Delaware Application December 3, 1952, erial No. 323,774 Claims priority, application Germany December 7, 1951 5 Claims. (Cl. 181-412) The present invention relates to a wide-band loudspeaker. Conventional type loudspeakers generally reproduce the frequency range above 6000 /8. unsatisfactorily. It is known to employ two loudspeakers for eliminating this drawback, i. e. a larger one for the low frequencies and a smaller one for the high frequencies. The low-frequency speakers often comprise a free radiating, electrodynamic system and the high-frequency speakers comprise a horn-loudspeaker. Further it is known to combine these loudspeakers to one unit.

Another method for improving the radiation of the high frequencies is to connect, in addition to the main diaphragm, a further unsupported radiating body, generally consisting of a more steep cone, to the driving coil.

Furthermore it is known to provide spring suspensions for the main diaphragm so that the outer parts of the main diaphragm are not vibrated by the higher frequencies. Thereby the vibrating mass of the diaphragm is reduced. These embodiments, however, are expensive and only partly effective.

In accordance with the present invention improved results are attained for providing a displacer which is attached in a resilient manner to the diaphragm, constituting together therewith a horn system. More specifically, the main diaphragm is provided in the center with an inset, which is preferably designed with its surface corresponding to that of a segment of a sphere. In a further development of the idea of the invention the spring suspension is provided with an attenuation means and the displacer may be furnished with a central exit aperture.

The invention will be particularly described with reference to the accompanying drawing, in which:

Fig. 1 shows schematically one embodiment of the invention for an improvement of the radiation of high frequencies; and

Fig. 2 shows another embodiment.

The main diaphragm 1 is provided in the center with an inset 2 which may be in the shape of a spherical cap. In front of this inset there is a displacer 3 which is attached via spring suspensions 4 to the main diaphragm. The displacer 3, which has as little mass as possible constitutes together with the main diaphragm a horn. The spring suspensions 4 are so proportioned that together with the mass of the displacer 3 there results a resonant frequency lying, for instance, at about 2000 C./ S. Below this frequency the displacer practically completely carries out all vibrations of the main diaphragm together therewith and there are no relative movements between the spherical cap and the displacer. Above the resonant frequency the displacer remains more and more quiet; pressure fluctuations appear between the displacer and the spherical cap, which are radiated through the horn. The matching of the horn resistance to the resistance of the diaphragm is possible in the conventional manner by correspondingly selecting the relation of the spherical cap surface to the initial cross-section of the horn.

Instead of having the shape represented in Fig. l, the displacer may be provided with a central exit aperture 5 as shown in Fig. 2. In order to obtain a smooth frequency curve the resonance of the displacer is required to be sufliciently attenuated. This is achieved by employing a suitable material for the spring suspensions 4 which. in the most simple case, consist of paper. If materials Patented Sept. 6, 1955 with slight deformation losses are employed, then an additional attenuation has to be provided for. Paper, balsa wood, or like material having a density in the range of .l0-1.2 gms./cu. cm. are suitable for making the displacer, a requirement being that the material has sufficient stiffness to maintain its shape. The spherical cap should be hard enough to be self supporting and may consist of paper glass, phenolresin compound, lucite, or other materials that will be light weight and stiff.

An advantage of the arrangement consists in its simplicity. Only one driving coil and only one diaphragm are used. Owing to the fact that the displacer and the diaphragm move together more or less as a unit; it is possible to make the space between spherical cap and displacer small, without danger of contact between them and resulting in modulation between low and high frequencies.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

l. A loudspeaker comprising a vibratory diaphragm having a reduced neck portion which is closed by an insert, said diaphragm and insert providing a frequency response which substantially drops off above a predetermined frequency range, a displacer member, means resiliently attaching said displacer member at its periphery to the said vibratory diaphragm adjacent to said neck portion but held in spaced relation to said insert, the mass of said displacer and the resiliency of said attaching means being proportioned so that below said frequency range said displacer and diaphragm vibrate effectively as a unit, while above said frequency range the displacer remains relatively quiet, and a single moving coil attached to said neck portion to operate said diaphragm and displacer.

2. A loudspeaker according to claim 1 in which said insert is in the shape of a spherical sector and said displacer has a complementary shaped surface in spaced relation to said insert to provide a substantially uniform spherical gap between said insert and displacer.

3. A loudspeaker according to claim 2 in which said displacer is substantially conical in shape with the apex thereof facing the exit mouth of the loudspeaker and the base thereof in spaced relation to said insert.

4. A loudspeaker according to claim 1 in which said displacer member has a horn shaped opening extending through the body thereof with the longitudinal axis thereof in substantial alignment with the center of said insert.

5. A loudspeaker comprising a main vibratory diaphragm having a reduced neck portion which is closed by an insert, means defining a closed chamber located in front of said insert, the said means comprising a plug which is flexibly attached to the reduced neck por tion of said diaphragm to define a narrow air gap between the plug and said insert, and a single moving coil fastened to said reduced neck for moving said diaphragm and plug as a unit for frequencies up to a predetermined range while enabling said plug to remain substantially quiet with respect to said diaphragm for frequencies above said range.

References Cited in the file of this patent UNITED STATES PATENTS 1,907,723 Bostwick May 9, 1933 2.007,747 Ringel July 9, 1935 2,231,479 Perry Feb. 11, 1941 2,256,270 Swift Sept. 16, 1941 2,269,284 Olson Jan. 6, 1942 

